He said North Korea had been “getting away with a tragedy that can’t be allowed”.

But he declined to say whether the US was considering a pre-emptive military strike, arguing that his administration never discusses such deliberations publicly. Mr Trump said it was time that somebody stood up to the pariah nation.

Flanked by US vice president Mike Pence, he said: “It may very well be tougher than I said.”

Mr Trump said the US “of course” would always consider negotiations with North Korea, but added that negotiations with the North have failed for the last 25 years. He accused his predecessors of failing to effectively address the North Korea problem.

Alluding to the threats against Guam, Mr Trump said if North Korea took any steps to even think about an attack, it would have reason to be nervous. “Things will happen to them like they never thought possible, OK?” Mr Trump said. Of North Korean leader Kim Jong-un, Mr Trump added: “He’s been pushing the world around for a long time.”

North Korea yesterday announced a detailed plan to launch a salvo of ballistic missiles toward Guam.

The announcement included the claim that the North is finalising a plan to fire four of its Hwasong-12 missiles over Japan and into waters around the tiny island, which hosts 7,000 US military personnel on two main bases and has a population of 160,000.

It said the plan could be sent to Mr Kim for approval within a week.

Japan and South Korea vowed a strong reaction if the North were to go through with the plan.

The plan involves the missiles hitting waters 19 to 25 miles from the island. It is unclear whether – or exactly why – North Korea would risk firing missiles so close to US territory. Such a launch would almost compel the US to attempt an intercept and possibly generate further escalation.

North Korea, no stranger to bluffing, frequently uses extremely bellicose rhetoric with warnings of military action to keep its adversaries on their heels.

It generally couches its threats with language stating it will not attack the United States unless it has been attacked first or has determined an attack is imminent.

But the statement raised worries amid threats from both sides.

Guam lies about 2,100 miles from the Korean Peninsula, and it is extremely unlikely Mr Kim’s government would risk annihilation with a pre-emptive attack on US citizens.

It is also unclear how reliable North Korea’s missiles would be against a distant target.